xrr radiography 2006

8/12/2019 XRR Radiography 2006

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RefresherRefresher ofof

Radiation SafetyRadiation Safetyfor Radiography Usersfor Radiography Users

www.temple.edu/ehs/training.htmlwww.temple.edu/ehs/training.html
http://www.temple.edu/ehs/training.htmlhttp://www.temple.edu/ehs/training.htmlhttp://www.temple.edu/ehs/training.html


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Quantities and UnitsQuantities and Units


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Radiation QuantitiesRadiation QuantitiesExposureExposure Intensity ofIntensity of

xx--rayray

11 C/kgC/kg =3876=3876 RR

DoseDose EnergyEnergy

absorbed perabsorbed per

unit massunit mass

11 GyGy = 100= 100 radrad

DoseDose

EquivalentEquivalent

Dose * QDose * Q

(Q=1 for x(Q=1 for x--ray)ray)

11 SvSv= 100= 100 remrem


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Entrance dose & Effective doseEntrance dose & Effective doseEntrance doseEntrance dose::

Skin doseSkin dose

Absorbed dose at skinAbsorbed dose at skinEffective doseEffective dose::

AA calculated dose quantitycalculated dose quantityreflecting the effectivereflecting the effectiveenergy absorbed by the bodyenergy absorbed by the body

taking into consideration the different sensitivitytaking into consideration the different sensitivityof organs to radiationof organs to radiation

Best representation for risk of dose to our bodyBest representation for risk of dose to our body


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Dose LevelsDose Levels


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Examples ofExamples of typicaltypical dose levelsdose levelsAv. BackgroundAv. Background (in US)(in US)

(~2/3 from Radon gas)(~2/3 from Radon gas)

300300 mremmrem per yearper year

~ 1~ 1 mremmrem per dayper day

Chest XChest X--ray (PA)ray (PA) 22 mremmrem (effective dose)(effective dose)

1313 mremmrem (skin dose)(skin dose)

Abdomen CTAbdomen CT 5,0005,000 mremmrem (effective dose)(effective dose)12,00012,000 mremmrem (skin dose)(skin dose)

FluoroscopyFluoroscopy 5,8005,800 mremmrem (skin dose)(skin dose)for a 24 minfor a 24 minvertebroplastyvertebroplasty

LDLD--5050 (Lethal dose for(Lethal dose for

50% population in 30 days)50% population in 30 days)

250,000250,000450,000450,000 mremmrem to theto the

whole bodywhole body


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Biological Effect ofBiological Effect of

RadiationRadiation


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Stochastic effectStochastic effect : : No threshold doseNo threshold dose

Higher the dose, higher the probability ofHigher the dose, higher the probability ofeffecteffect

Basis for radiation safety in medical fieldBasis for radiation safety in medical field

Example: leukemia, thyroid cancer, breastExample: leukemia, thyroid cancer, breast

cancercancer

Risk of radiation induced mortality 5% perRisk of radiation induced mortality 5% per SvSv


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Deterministic effectDeterministic effect : :There is threshold dose, typically a high dose toThere is threshold dose, typically a high dose to

localized area of the bodylocalized area of the body

Example:Example:

erythemaerythema---- threshold dose 2threshold dose 2 GyGy(200,000(200,000 mremmrem))

cataractcataract---- threshold dose 1threshold dose 1 GyGy(100,000(100,000 mremmrem))


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Sensitivity to radiationSensitivity to radiation:: Greater sensitivity for cells that multiplyGreater sensitivity for cells that multiply

more rapidlymore rapidly Lymphoid, gonads, bone marrow, bowels,Lymphoid, gonads, bone marrow, bowels,

thyroidthyroid Fetuses and young children are moreFetuses and young children are more

susceptible to radiation injurysusceptible to radiation injury


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Regulatory dose limitsRegulatory dose limits


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Dose limit from NRCDose limit from NRC

General PublicGeneral Public::

100100 mremmrem (effective dose) per year(effective dose) per year22 mremmrem in 1 hourin 1 hour

Radiation WorkerRadiation Worker::5,0005,000 mremmrem per yearper year total effective dosetotal effective dose


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Pregnant radiation worker andPregnant radiation worker and

patientpatient Pregnant radiation workerPregnant radiation worker::

Regulatory dose limit for embryo/fetusRegulatory dose limit for embryo/fetus::500500 mremmrem throughout the entire pregnancythroughout the entire pregnancy

Worker can declare pregnancy voluntarily and inWorker can declare pregnancy voluntarily and inwriting to Radiation Safety Department, she willwriting to Radiation Safety Department, she will

then receive counseling and evaluationthen receive counseling and evaluation


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Principle from NRCPrinciple from NRC

ALARAALARA==

AAss LLowowAAss RReasonablyeasonablyAAchievablechievable


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ALARA limitsALARA limits

125125 mremmrem/month/month for technologistsfor technologists

and residentsand residents

375375 mremmrem/month/month for cardiologistsfor cardiologists

and interventional radiologistsand interventional radiologists

User will be notified if ALARA limit isUser will be notified if ALARA limit isexceededexceeded


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Minimizing RadiationMinimizing Radiation

ExposureExposure


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Minimize Radiation ExposureMinimize Radiation Exposure

TimeTime

Minimize time exposed to xMinimize time exposed to x--rayray DistanceDistance

Stay back from the beam & source of scatteringStay back from the beam & source of scattering ShieldingShielding

AA 0.5 mm0.5 mm leadlead--equivalent garment attenuateequivalent garment attenuate>95%>95% of scattered exposureof scattered exposure

AA 0.3 mm0.3 mm leadlead--equivalent garment attenuatesequivalent garment attenuates

>>75%75% of scattered exposureof scattered exposure


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ShieldingShielding

UtilizeUtilize the shielding equipmentsthe shielding equipmentsavailable to youavailable to you

Most wall barriers have at least 1/32Most wall barriers have at least 1/32(0.79 mm) lead lining, windows have(0.79 mm) lead lining, windows have0.5 mm lead equivalent or more0.5 mm lead equivalent or more

0.5 mm0.5 mm PbPb equivalent reduces >95%equivalent reduces >95%scattered exposurescattered exposure


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Leaded GarmentsLeaded GarmentsAll leaded garments areAll leaded garments are surveyed withsurveyed with

fluoroscopyfluoroscopywhen first acquired andwhen first acquired and

annuallyannuallythereafter (see tags for surveythereafter (see tags for survey

date and initials)date and initials)

Garments will not be in service if thereGarments will not be in service if thereareare holes > 3 mmholes > 3 mm oror tears > 3 cmtears > 3 cm thatthat

covers sensitive areas.covers sensitive areas.


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Major source of radiation exposureMajor source of radiation exposure

for most radiation workers:for most radiation workers:ScatteringScattering from the patientfrom the patient

Unshielded operator standingUnshielded operator standing 1 foot1 foot awayawayfrom source of scattering receivesfrom source of scattering receives ~1%~1% ofof

the entrance exposure of the patientthe entrance exposure of the patient((1 meter1 meter awayaway---- ~~0.1%0.1% entrance exposure)entrance exposure)

BackscatteringBackscattering(towards the source) has(towards the source) hashigher intensity for clinical range Xhigher intensity for clinical range X--rayray

Forward scattering is alsoForward scattering is also attenuated by theattenuated by thepatientpatient


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HigherHigher kVpkVp

Higher energy of the photonsHigher energy of the photons

More penetration (for larger patient)More penetration (for larger patient) Lower skin doseLower skin dose

Higher deep doseHigher deep dose Reduces LowReduces Low--Contrast ResolutionContrast Resolution

In chest radiography, highIn chest radiography, high kVpkVp reducesreducescontrast between tissue and bone (ribscontrast between tissue and bone (ribsappear more transparent)appear more transparent)


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HigherHigher mAmAoror mAsmAs

For larger body parts or larger patientsFor larger body parts or larger patients

(much higher scattered radiation)(much higher scattered radiation) Higher dose (Higher dose (in linear proportion toin linear proportion to mAsmAs))

LowerLower noise levelnoise level in the CR/DR image (asin the CR/DR image (aslong as not overlong as not over--saturated)saturated)

There should be aThere should be a balancebalance betweenbetweenabsorbed dose and acceptable noise level.absorbed dose and acceptable noise level.

Darker image on filmsDarker image on films


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DistanceDistance ShorterShorter SSD (source to skin distance)SSD (source to skin distance)

gives higher dose; longer SSD reducesgives higher dose; longer SSD reduces

unsharpnessunsharpness due to the finite size of focaldue to the finite size of focalspotspot

Object to image (patient to imageObject to image (patient to imagereceptor) distancereceptor) distance should always beshould always be

minimizedminimized for less scattering, lower dose,for less scattering, lower dose,and better image qualityand better image quality


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FiltrationFiltration of Xof X--rayray

AttenuatesAttenuates lowlow--energyenergy photons which dophotons which do

not contribute to imagingnot contribute to imaging hardening of xhardening of x--ray beam gives higher %ray beam gives higher %

depth dosedepth dose Reduces skin doseReduces skin dose

Reduces intensity of xReduces intensity of x--rayray


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CollimationCollimation

Reduces integral doseReduces integral dose

Reduces scatteringReduces scattering Sharper imageSharper image


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Information forInformation forSpecific modalitiesSpecific modalities


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RadiographyRadiography && PodiatryPodiatry


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Computed RadiographyComputed Radiography ((CRCR) &) &

Digital RadiographyDigital Radiography ((DRDR))

vsvsScreenScreen--film Radiographyfilm Radiography

CR and DR doCR and DR do notnot use filmsuse films


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Computed RadiographyComputed Radiography ((CRCR)) CassetteCassette is image plate made of (PSP )is image plate made of (PSP )

photostimulablephotostimulable phosphor detector systemphosphor detector system

Image plate is scanned by laser beam, theImage plate is scanned by laser beam, the

light released is collected and converted tolight released is collected and converted to

electronic signal which is digitizedelectronic signal which is digitized

HasHas much wider latitudemuch wider latitude than screenthan screen--filmfilm

system; thereforesystem; therefore eliminate retakes due toeliminate retakes due tooverover--exposure or underexposure or under--exposureexposure..


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Digital RadiographyDigital Radiography ((DRDR))

Cassette isCassette is notnot neededneeded

UseUse indirect detectionindirect detection flat panelflat panelsystem (withsystem (with CsICsI screen)screen) oror seleniumselenium

direct detectordirect detector, coupled to TFT (thin, coupled to TFT (thin--film transistor) detector elementsfilm transistor) detector elements

Flat panelFlat panel direct detectorsdirect detectors shouldshouldreducereduce radiation dose, but.radiation dose, but.

Nationwide Evaluation of XNationwide Evaluation of X-rayray


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Nationwide Evaluation of XNationwide Evaluation of X--rayray

TrendsTrends ((NEXTNEXT)) Facilities with CR/DRFacilities with CR/DR tendtend to useto use

techniques givingtechniques giving higherhigher doses todoses topatients than facilities with traditionalpatients than facilities with traditional

screenscreen--filmfilm

2001 Chest Radiography survey:2001 Chest Radiography survey:

ScreenScreen--film:film: 0.120.12 mGymGyentent. skin. skin kermakerma

CR & DR: 0.16CR & DR: 0.16 mGymGyentent. skin. skin kermakerma


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Digital ImagesDigital Imagesvsvs screen/filmsscreen/films

Digital images haveDigital images have lower spatiallower spatial

resolutionresolution due to limitation in numberdue to limitation in number

of pixelsof pixels

Digital images haveDigital images have better lowbetter low--contrastcontrastresolutionresolution due to availability ofdue to availability of

windowing and leveling, lead towindowing and leveling, lead toimproved interpretation & diagnosisimproved interpretation & diagnosis


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Patient DosePatient Dose in radiographyin radiography

ProtocolProtocol NEXTNEXT

EntranceEntranceExposureExposure

((mRmR))

PA ChestPA Chest 16.116.1

AP Lumber SpineAP Lumber Spine 370370

AP AbdomenAP Abdomen 310310

Patient DosePatient Dose inin


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Patient DosePatient Dose inin

podiatric radiographypodiatric radiographyViewView

((SID=28SID=28))

kVkV mAmA Time (s)Time (s) EntranceEntrance

ExposureExposure

((mRmR))

Foot, APFoot, AP 5050 1515

1515

0.40.4 1616

Foot, LatFoot, Lat 5454 0.450.45 2323

* Higher dose than regular radiographic units

(which typically use 60 kV & 3 mAs at 40 SIDfor extremities)

xrr radiography 2006

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